getDevice(0) returns null

[mauro]

Hi

i downloaded the source code and compiled Tester.java under ubuntu linux.
When i run the Tester class
connection.getNumberDevices() returns 1, but
connection.getDevice(0) returns null

What should I check?

Thanks,
Mauro

[Andi McLean]

This is a rather interesting problem.

Have you tried
connection.getDevices();

which returns a vector of devices?

and check the size of that and if it contains the device?

Andi

[mauro]

I have modified the tester class to include a call to connection.getDevices().

    public Tester()
    {
        try
        {
            JSane_Net_Connection connection = new JSane_Net_Connection("127.0.0.1", 6566);

            System.out.println("> calling connection.getDevices()");

            Vector v = connection.getDevices();

            System.out.println("> end of connection.getDevices()");

            int size = v.size();

            System.out.println("size of connection.getDevices() => " + size);

            for (int deviceNum = 0;
                deviceNum < connection.getNumberDevices();
                ++deviceNum)
            {

            ....
            ....

connection.getDevices() returns an empty vector, while getNumberDevices() still returns 1.

In fact getDevices calls getNumberDevices which tests if _devices == null and since this happens it calls
_devices = net_get_devices();

The net_get_devices() method issues

reply.devices = _wire.getPtrArray( dev );

The getPtrArray method calls

int size = getWord();

This call returns 1, so getWord is called a second time

isNull = getWord();

and it returns 1 this time too, so

vec.add(null)

is executed.

As a result the _devices.devices Vector has one element and this element is null. This explains why
getNumberDevices returns 1 and getDevices() returns an empty vector.

But i cannot explain why my device is not correctly detected.

I enclose a log i have made (here also getWord is logged).

> calling connection.getDevices()
> start of getNumberDevices
_devices == null
> start of net_get_devices
1st getbyte returns => 0
value is => 0
2nd getbyte returns => 0
value is => 0
3rd getbyte returns => 0
value is => 0
4th getbyte returns => 0
value is => 0
> start of getPtrArray
1st getbyte returns => 0
value is => 0
2nd getbyte returns => 0
value is => 0
3rd getbyte returns => 0
value is => 0
4th getbyte returns => 1
value is => 1
> 1st getWord returns => 1
1st getbyte returns => 0
value is => 0
2nd getbyte returns => 0
value is => 0
3rd getbyte returns => 0
value is => 0
4th getbyte returns => 1
value is => 1
> 2nd getWord returns => 1
> getPtrArray returns a vector with size => 1
first element of returned Vector is null
> end of getPtrArray
> end of net_get_devices
getNumberDevices: _devices.devices has size => 1
first element of _devices.devices is null
> start of getNumberDevices
> end of connection.getDevices()
size of connection.getDevices() => 0

I hope you can give some help.

Thanks, Mauro

[mauro]

i believe the scanner is correctly installed because we can scan with scanimage

[mauro]

also, in net_get_devices i get reply.status = 0 (= SANE_STATUS_GOOD)

[Andi McLean]

Thanks for the debugging.

I'll add a check to make sure that null is not entered in to the vector.

Have you tried performing scanimage -L on the same box as you are trying to run JSane and checking that the device is listed with a net: interface.

Andi

[mauro]

it was a kind of problem with permissions, we have solved by starting saned with user = root and group = root.

Mauro